help me find issues in my code gps baseband

Altera_Forum · ‎06-13-2014

I was hoping others here could help me identify issues in my code modules. I beleive I may have timing/metastability issues but I am not certain. These modules are part of a gps receiver project I've been working on.

sysclk = 50 MHz main real clock on fpga

sampleclk = 5 MHz by 10 counter divider, durration 1 sysclk cycle

My CA code generator


module CAcode(nextChip, sysclk, reset, Tap1, Tap2, chip, codeReset, codeDelay);
 input reset;
 input sysclk;
 input nextChip;
 input Tap1; //bits needed for index
 input Tap2; //bits needed for index
 input codeDelay;
 output chip;
 output reg codeReset;  //readable on sysclk
 reg  G1;
 reg  G2;
 reg  chipCount;
 reg flagReset;
 reg countDelay; 
 
 always @ (posedge nextChip) //must be on posedge to maintain correct freq of chip rate
 begin 
 
  chipCount <= chipCount + 12'd1;
  G1 <= {G1, (G1 ^ G1)}; //shifts 9 and xors last bit
  G2 <= {G2, (G2 ^ G2 ^ G2 ^ G2 ^ G2 ^ G2)};//shifts 9 and xors last bit
  
  if(chipCount > 1023)
  begin
   chipCount <= 0;
   G1 <= 10'b1111111111; //initialize G1
   G2 <= 10'b1111111111; //initialize G2
   flagReset <= 1;
   countDelay <= 0;
  end
  else flagReset <= 0; //flagReset takes 1.023MHz timing to reset to 0
  
//if in search mode, delay is always active, inactive in track mode
//should cause 1 chip delay in code from normal reset timing ???
  if(codeDelay)
  begin
   if(countDelay == 0 && chipCount == 1) //effectively delays code by 1 chip ever start of millis cycle
   begin
    chipCount <= 0;
    countDelay <= 1;
    G1 <= 10'b1111111111; //initialize G1
    G2 <= 10'b1111111111; //initialize G2
   end
  end
 end //of nextChip
 
 always @ (posedge sysclk) //should make certain codeReset is readable on a sysclk 
 begin
  codeReset <= flagReset; //may be several sysclk cycles long
 end
 
 assign chip = G1 ^ G2 ^ G2; //set current chip output
endmodule   //CA code

My code timing NCO


//This is proven to chip at desired rate by oscilliscpoe
module NCO_chipRate(sysclk, reset, cntl_word, chip_enable, nextChip, nco_val, get_nco_val);
 input sysclk, reset;
 input  cntl_word;
 input get_nco_val;
 output chip_enable; //late, prompt,early
 output nextChip;
 output reg nco_val;
 reg  advanceFlag;
 reg   chip_status;
 reg    accum_reg;
   reg    cycle_count_reg;
   wire   phase_key;
   wire   accum_sum;
   wire accum_carry;
   wire   combined_carr_value;
 
 // 30 bit phase accumulator
   always @ (posedge sysclk)
 begin
  if (reset) 
  begin
   accum_reg <= 0;
   cycle_count_reg <= 0;
  end
  else 
  begin
   accum_reg <= accum_sum + cntl_word;
   if (get_nco_val)
   begin
    nco_val <= combined_carr_value; // latch in carrier value, then...
    cycle_count_reg <= 0; // reset counter
   end
   else if (accum_carry) 
   begin
    cycle_count_reg <= cycle_count_reg + 1'b1;
   end
  end
 end 
 // outputs half and full chip signal per cycle
 always @ (posedge sysclk) // 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
 begin
  if(phase_key == 4'd4)
  begin
   chip_status <= 1;
   chip_status <= 0;
   chip_status <= 0;
  end
  else if(phase_key == 4'd8)
  begin
   chip_status <= 0;
   chip_status <= 1;
   chip_status <= 0;
  end
  else if(phase_key == 4'd12)
  begin
   chip_status <= 0;
   chip_status <= 0;
   chip_status <= 1;
  end
  if(phase_key == 4'd15) advanceFlag <= 1; //signal to advance chip coder
  else advanceFlag <= 0;
 end
 
 assign accum_sum = accum_reg; 
 assign accum_carry = accum_sum;
 assign phase_key = accum_sum;
 
 //for controller value reading
 assign combined_carr_value = accum_reg;
 assign combined_carr_value = cycle_count_reg;
 assign nextChip    = advanceFlag;
 assign chip_enable = chip_status;
endmodule

my adder section partial code


//update current chip value on time signal
 always @ (posedge chip_enable) //early
 begin
  Echip <= chip_in;
 end
 always @ (posedge chip_enable) //prompt chip
 begin
  Pchip <= chip_in;
 end
 always @ (posedge chip_enable) //late
 begin
  Lchip <= chip_in;
 end
////////////////////////////  generated CARRIER MULTIPLY /////////////////////////////
 //this multiplies Imag, Qmag input by generated carrier split I/Q
 assign i_mix = !Iin;
 assign i_mix =  Iin | Igen;
 assign i_mix =  Iin & Igen;
 assign q_mix = !Qin;
 assign q_mix =  Qin | Qgen;
 assign q_mix =  Qin & Qgen;
 //multiplies Isign and Qsign with generated carrier split I/Q
 //instead of like sign cancelling it produces a positive resultAng
 //unlike signs produce negative result
 assign q_sign   =  !(Qin ^ Qgen);
 assign i_sign   =  !(Iin ^ Igen);
 
////////////////////////   data ADDER portion   /////////////////////////////
 always @ (posedge sampleclk)
 begin
  //put newest value into shift register
  buff_Qearly <= {buff_Qearly, (q_sign ^ Echip)};
  buff_Iearly <= {buff_Iearly, (i_sign ^ Echip)};
  //add newest to sum and subtract oldest from sum
  sum_Iearly <= sum_Iearly + buff_Iearly - buff_Iearly;
  sum_Qearly <= sum_Qearly + buff_Qearly - buff_Qearly;
  //put newest value into shift register
  buff_Qprompt <= {buff_Qprompt, (q_sign ^ Pchip)};
  buff_Iprompt <= {buff_Iprompt, (i_sign ^ Pchip)};
  //add newest to sum and subtract oldest from sum
  sum_Qprompt <= sum_Qprompt + buff_Qprompt - buff_Qprompt;
  sum_Iprompt <= sum_Iprompt + buff_Iprompt - buff_Iprompt; 
  //put newest value into shift register
  buff_Qlate <= {buff_Qlate, (q_sign ^ Lchip)};
  buff_Ilate <= {buff_Ilate, (i_sign ^ Lchip)};
  //add newest to sum and subtract oldest from sum
  sum_Qlate <= sum_Qlate + buff_Qlate - buff_Qlate;
  sum_Ilate <= sum_Ilate + buff_Ilate - buff_Ilate;
end  
always @ (posedge codeReset)
 begin
  if(sum_Iprompt > 2500) lock_flag <= 3'b001;
  //else if(sum_Iprompt > 2750) lock_flag <= 3'b011;
  //else if(sum_Iprompt > 3500) lock_flag <= 3'b111;
  else lock_flag <= 3'b000;
 end

Any and all constructive criticisim is welcome.